A friend of mine posted a link on the topic "Eleven Spiritual Books," and it prompted me to type out some thoughts of my own along these lines. Rather than specify eleven books, I decided it would be more natural to write about four general areas.
Myth/Shamanism
Almost as soon as I could read, I gravitated to fairy tale, mythology and even material associated with the major religions of the world. Finland's major myth tale cycle, The Kalevala, and Wales' The Mabinogi, have strongly resonated with me for many years. Decades after first reading them, I heard recordings of native speakers read aloud what seems to be a dim shadow in translation. Both song-poems involve a world view that is animistic and transformative, suggesting development and a space-time continuum that isn't linear and, in fact, explicitly mysterious. George MacDonald's Phantastes has something of these qualities, along with influence of Germanic Faerie Tale. One can hear similar echoes in the best of High Fantasy, particularly the enduring masterpieces of J.R.R. Tolkien.
Theatre/Ritual
Peter Kingsley's works represent a radical reinterpretation of the foundations of Western Civilization. Could it be that Plato and Aristotle deliberately distorted and obfuscated the rich spiritual tradition of the largely matriarchal Persian mystery cults as explicated in the works of Parmenides, Empedocles and others? Hesychia (Greek for "stillness") might be likened to the trance states of ancient shamans, tools for self-transformation in Western magick, and to Buddhist meditation.
One book I read 30 years ago was Peter Brook's brilliant The Empty Space. Given the connections between ritual, magick and theatre in the world from ancient times, through the Renaissance, and to today, in retrospect I can see the relevance of Brooks' musings on the Deadly, Holy, Rough and Immediate Theatre to all things spiritual.
Which is the perfect lead-in to Shakespeare, Marlowe, and all the great poets. Through ritual & magic, players transform into Kings, Queens, Fools and Monsters. Words, words, words.
Hermeticism, Alchemy, QBL, & Western Magick
When I consider what I think is a basic list of works for this section, including The Emerald Tablet, Agrippa's Three Books of Occult Philosophy, Ficino, Giordano Bruno, Paracelsus, John Dee, modern scholars such as Frances Yates, Mircea Eliade, Brian Copenhaver, modern occult/mystics including the Theosophists, Golden Dawn, Crowley, Gurdjieff, and Carl Jung, a few major themes arise.
One, that there's many tools out there for self-realization and inner transformation. Two, there's the suggestion in Jung and elsewhere that these tools are archetypal, thus by their nature metaphorical, not literal. Thus, the "Gods" or "Planets" and so on are psychological states within. There's as many such states possible within as there are stars in the sky. Third, there's the influence on the West from spiritual paths in the East.
One, that there's many tools out there for self-realization and inner transformation. Two, there's the suggestion in Jung and elsewhere that these tools are archetypal, thus by their nature metaphorical, not literal. Thus, the "Gods" or "Planets" and so on are psychological states within. There's as many such states possible within as there are stars in the sky. Third, there's the influence on the West from spiritual paths in the East.
West Meets East
Many of the writers from the previous section included some of the first Westerners to explore Eastern paths. Take Aleister Crowley's Eight Lectures On Yoga. Two modern takes I like include Robert Aitken's Mind Of Clover, which lays out basic Zen Buddhist Philosophy, and suggests "Middle Paths" Westerners might adopt. Also, David Reynold's Playing Ball On Running Water boils down a Zen Buddhist approach to very simple terms: emotions are vital, but the only way to have some degree of control in one's life is to do what needs to be done next.
Finally, in 2009, I was curious about the teachings of Vietnamese Buddhist Master Thich Nhat Hanh, so I surveyed the shelves at the library, and one book really stood out for me: his 2005 tome, Teachings On Love. I happened to read this work during a very turbulent year in my life. One chapter in Thich's book addressed something that was very central to me. He began talking about how we know love, and the first experience most of us have of love: from our mothers. I found out my mother had died in a way that was sudden and shocking, and even though it was six months after the fact, I was still dealing with her loss. That chapter in particular helped me realize that of all the gifts my mother gave me, the most valuable one was the capacity to love.